The present invention relates to a method of burning a fuel in the presence of an oxidant in which intermixing fuel and oxidant jets are formed from fuel and oxidant flowing in a mixing layer. More particularly, the present invention relates to such a method and apparatus in which the mass flow rates of the fuel or the oxidant or both are intermittent and have regular pulsations of a sufficiently high frequency that an even distribution of fuel-rich and fuel-lean regions are created throughout a projected flame produced from combustion of the fuel and oxidant.
Burners in which fuel is burned in an oxidant, for instance, air, oxygen-enriched air, or oxygen, are utilized in many industrial processes where it is necessary to heat a melt. The burning of a fuel produces a pollutant known as thermal NO.sub.x. The mount of thermal NO.sub.x produced reaches a maximum when the fuel is burned in stoichiometric proportions.
It is known in the an that if the fuel is either burned sub-stoichiometrically or super-stoichiometrically, thermal NO.sub.x emissions will be reduced. In line with this, Australian Patent No. 9220395 discloses a burner for an industrial furnace in which either the fuel, or oxidant or both is pulsated at a frequency of lower than 3 Hz, typically lower than 1 Hz. This has been found to reduce NO.sub.x emissions. At frequencies above 3 Hz, measured carbon monoxide emissions were found to increase and hence, a preferred frequency lower than 3 Hz was established for the burner. The burner of Australian Patent No. 9220395 is a relatively complex mechanical instrument that is fed by a duct work having valves which must continually open and close periodically at the desired pulsation frequency.
As will be discussed, the present invention provides a pulsation driven burning method and apparatus that is capable of operating at higher frequencies than the Australian '395 application with attendant low NO.sub.x and low carbon monoxide production. Additionally, the present invention provides a burner that is capable of pulsating combustion with far less complexity than prior art burners designed to pulsate fuel and/or oxidant.